Utilizing load elements to which strain gauges are attached for supporting a platform such as might be used as a weighing scale are well known in the art although for many applications, they have not been wholly accepted. In certain heavy duty applications such as truck weighing or thrust measurements, load elements with attached strain gauges are sometimes the only practical means of providing an indication of the forces involved. In various other better known applications such as postage weighing scales, meat counter scales and the like wherein the loads are much lighter problems have arisen primarily as a result of off-center loading on the platform of the object to be weighed.
Improved design of the load elements as well as the associated strain gauges wherein means are included which will isolate the load element and strain gauges from extraneous forces such as undesirable moments and side forces created by an off-center loading have been proposed.
While effective isolation of undesired moments and side forces from off-center loading can be achieved, the primary and most troublesome problem in weighing scales incorporating load elements and strain gauges is the fact that the sensitivities of each of the load elements and their associated strain gauges are not equal. Even though the load element itself, either in the form of a column or bending web or even a shear plate may be made identically to each other for supporting the weighing platform at various locations and even though strain gauges themselves can be manufactured within fairly close tolerances, when the device is completely assembled, more often than not the actual output signal from the electrical bridge incorporating the strain gauges changes when the load is shifted to different off-center positions.
With respect to the foregoing, it should be understood that the output signal is directly proportional to the applied load but the slope of the output signal which constitutes a measure of the sentivity will more often than not be different when the position of the load is shifted. If there were some means of equalizing the slope of the output signal for all positions of the load or force, then errors as a consequence of off-center loading on the platform resulting from different sensitivities of the supporting load elements would be wholly eliminated.